1. Field of the Invention
The invention concerns a method for controlling an actuator, in particular of a motor vehicle. The invention further relates to a motion system for controlling an actuator.
2. Description of the Background Art
In a motion system for an actuator of a motor vehicle, for example in a window regulator system, it is generally necessary to move the associated actuator into a defined location where the actuator is located in a stable position under predefined mechanical loads. This may be, for example, a closed position or an end position of the actuator. Thus, for example, the window of a vehicle door in the closed state must be moved into an end position, wherein the holding force of the window with respect to the adjacent seal must be large enough to compensate for the force of the weight and associated supporting parts, and keep the window stable and hold it closed. In particular, wind noise while driving should be avoided. In a sunroof, too, stability and tightness of seal are vital criteria that determine the requisite holding force. Since the weight is essentially supported by the sunroof itself, the requisite holding force is comparatively small, however. The stationary holding forces actually present in displacement systems of this type are typically greater than the forces that would be necessary for optimal fulfillment of the retaining function, however, since the actuator usually must overcome counteracting forces from a closure element or a seal in order to reach the end position.
In such a motion system, the actuator designed for displacement is typically moved into the mechanical end position with a maximum torque of the associated drive. The maximum torque of the drive must be large enough that the actuator can overcome, during movement, counteracting forces, such as, e.g., resistance counter to the direction of displacement exerted on a window by rubber seals.
In order to realize anti-pinch protection, motion systems are known in which a drive parameter, in particular a torque, is detected as a function of the position of the actuator, and in the case of an irregular deviation from normal behavior, the conclusion is drawn that a case of pinching (or jamming) is occurring. In this case, a predetermined association between the size of the drive parameter and the position of the actuator must be provided, since variations in the drive parameter along the displacement path are to be expected even during normal operation on account of mechanical deficiencies. Thus, for example, during displacement of a side window along a predetermined path, the resistance exerted by the mechanism counter to the direction of displacement can vary in magnitude as a function of position. In this regard, it is important to the functionality of the anti-pinch protection for the real position of the actuator to be known. To this end, a conclusion as to the real position is generally drawn from the number of rotations of the drive, which calls for calibration by means of a reference position.
For the purpose of calibration, the drive is switched off, for example after a specified time has elapsed after the end position has been reached, and the end position is associated with the direction of displacement as a reference position. In order to fulfill the retention function, the actuator is typically moved to the end position using the maximum torque of the drive, and the drive is switched off. In particular, in the case of a self-locking transmission or as a result of the necessary restoring forces against a switched-off drive, the actuator remains essentially in the end position, with the last applied drive torque as the restraining torque, except for an independent partial relaxation of the system, for example resulting from restoring forces during switchoff or from a dissipation of overstresses through the system components or the absorption of such overstresses within system tolerances.
In the stationary state, a strong holding torque disadvantageously exerts a load on the components of the system, since counteracting forces are built up by the holding torque which act as deforming forces on the components if they are dissipated only inadequately or are not dissipated at all. Components in current use made of economical materials, such as plastics, are sensitive to long-term stationary mechanical effects and can be plastically deformed despite toughness and breaking strength. In a motion system, this can lead to faster wear and development of disadvantageous noise during operation. Especially in motion systems with anti-pinch protection using the above-described principle of operation, the position association of the actuator required for identification of a case of pinching can be impaired by stressed parts despite regular calibration. In the event of irregular or abruptly increased resistance, which is sensed by a control module, for example through a reduced speed of the drive or an increased torque, the drive can be erroneously reversed or stopped even when an actual case of pinching is not occurring. As a result, a window that must overcome the counteracting forces of a rubber seal acting over a planar area shortly before reaching the end position—outside of the region of a possible case of pinching—and that requires a high torque for this purpose can be stopped by activation of the anti-pinch protection if the position association is incorrect, so that the window no longer reaches the end position.